Although receptor binding techniques have been employed to study the regional and subcellular location of the opiate receptor(s) in the brain, little is known about its molecular characteristics. In order to investigate the molecular nature of the opiate receptor, specific photoaffinity labeling reagents derived from opiates and enkephalins will be synthesized. These irreversible tags will be used in studies designed (1) to determine the apparent molecular weight(s) of the opiate receptor(s), (2) to determine if opiate agonists and antagonists interact with the same or different membrane components and (3) to investigate the possibility of opiate receptor subtypes.